Swash pumps, engines, or flow meters with nutating disks have been known for more than 50 years. Yet only one commercialized swash pump, (“Genta”™ Fristam; Hamburg, Germany; based on patents by Heng and Thomas) is known. All of the prior art incurs a good deal of sliding friction particularly between the inner swash sphere and the opposing part-spherical sections of the housing, which results in high frictional losses, especially when pumping gases. Gas provides less lubrication than a liquid at the contacting faces of any seals or fluid exposed bearing faces. The frictionally generated heating is added to localised adiabatic heating when pumping a gas which itself detracts from cooling functions. Previous designs of swash pump have relied on precision manufacture to hold parts in close or sliding proximity for improved sealing, but are vulnerable to distortion of parts by thermal expansion and then possible pump seizure. Unlubricated wear also causes short parts life.
In particular, use of a rigid swash plate assembly with a rigid inner sphere, firmly yet slidably held between part spherical cavities, prevents true self-centering of the swash plate from occurring with respect to the opposing cone faces in response to manufacturing tolerances and thermal expansion, even though there may be a resiliently-mediated bias towards contact. The prior art design leads to high inner spherical contact friction and poor swash to cone sealing.
The present invention will be described in relation to a vapour extraction application inside a fuel dispenser, in order to illustrate a pump that is effective when used to pump a fluid. A vapour recovery function is a regulatory requirement imposed in an increasing number of countries. Explosive gas mixtures are required to be removed from the vicinity of the pump nozzle while a vehicle tank is being filled. The volumetric displacement of gas by this pump must by law or regulations be proportional to the volume delivery of liquid fuel. A relatively small tube ending in the nozzle head, within an outer metal tube or a rubber boot surrounding and sealing the vehicle tank opening is run along or inside the hose to the nozzle and is connected to the pump which usually returns the vapour to the vapour space above a fuel storage tank where condensation may occur and any excess air or vapour is exhausted through a carbon filter vent far from the fuelling event. Since the fuel/air mixture being pumped is flammable and explosive, the pump must not comprise a danger or detract from safety in any way. It is desirable that the pump neither causes any flame or explosion nor transmits any flame or explosion from the exterior or nozzle environment into the storage tank or visa versa.
At the present time, vapour recovery pumps use rotary vanes (Healy, USA), impellers, roller vanes (Pignone, Italy) or piston pumps (Durrtechnik, Germany). These pumps are relatively inefficient, some are noisy, and cannot handle slugs of liquid effectively. A “slug” of liquid is the liquid that will arrive at the pump from time to time, such as if the tank is over-filled or the filling pipe becomes full. A swash pump will cope with this circumstance.